Ms. Amita Shrestha Profile

Amita Shrestha

at Deutsches Zentrum für Luft und Raumfahrt eV

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Author

Publications (12)

Proceedings Article | 12 July 2023 Open Access

Effects of pointing errors on intensity losses in the optical LEO uplink

Andrea Carrillo-Flores, Dirk Giggenbach, Marcus Knopp, Davide Orsucci, Amita Shrestha

Proceedings Volume 12777, 127775U (2023) https://doi.org/10.1117/12.2691100

KEYWORDS: Satellites, Beam divergence, Signal intensity, Error analysis, Receivers, Astronomical imaging, Free space optics, Signal attenuation, Satellite communications, Data communications

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Proceedings Article | 12 September 2021 Presentation + Paper

QCalc: a tool to compute classical and quantum communication rates over free-space optical channels

Davide Orsucci, Jorge Rosano Nonay, Amita Shrestha, Florian Moll

Proceedings Volume 11868, 118680F (2021) https://doi.org/10.1117/12.2600016

KEYWORDS: Quantum key distribution, Free space optics, Receivers, Quantum communications, Sensors, Transmitters, Signal attenuation, Optical communications, Telecommunications, Satellites

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Proceedings Article | 20 September 2020 Presentation + Paper

Implementation of variable data rates in transceiver for free-space optical LEO to ground link

Jorge Pacheco-Labrador, Amita Shrestha, Julio Cesar Ramirez Molina, Dirk Giggenbach

Proceedings Volume 11532, 115320J (2020) https://doi.org/10.1117/12.2574390

KEYWORDS: Free space optics, Transceivers, Free space, Telecommunications, Data communications, Satellites, Data acquisition, Transmitters, Field programmable gate arrays, Satellite communications

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Proceedings Article | 7 October 2019 Paper

Stratospheric QKD: feasibility analysis and free-space optics system concept

Florian Moll, Thierry Botter, Christoph Marquardt, David Pusey, Amita Shrestha, Andrew Reeves, Kevin Jaksch, Kevin Gunthner, Oemer Bayraktar, Christian Mueller-Hirschkorn, Alberto Diago Gallardo, Dionisio Diaz Gonzalez, Wenjamin Rosenfeld, Peter Freiwang, Gerd Leuchs, Harald Weinfurter

Proceedings Volume 11167, 111670H (2019) https://doi.org/10.1117/12.2539076

KEYWORDS: Quantum key distribution, Free space optics, Telescopes, Adaptive optics, Electronics, Receivers, Atmospheric particles, Polarization, Atmospheric modeling, Telecommunications

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Quantum key distribution (QKD) is one of the most mature quantum technologies and can provide quantum-safe security in future communication networks. Since QKD in fiber is limited to a range of few hundred kilometers, one approach to bridge continental scale distances may be the use of high altitude pseudo satellites (HAPS) as mobile trusted nodes in the stratosphere. In parallel, free-space laser communication for high rate data transmission has been a subject of research and development for several decades and its commercialization is progressing rapidly. Important synergies exist between classical free-space communication and QKD systems since the quantum states are often implemented using the same degrees of freedom such as polarization or field amplitude and phase. These synergies can be used to benefit from the progress in classical free-space laser communication in QKD applications. In this paper, the use case of QKD in a stratospheric environment is described wherein HAPS may serve as relay station of secret keys and encrypted data. The mission scenario and HAPS capabilities are analyzed to derive special requirements on the stratospheric laser terminal, the link geometry and the ground segment with respect to a feasibility demonstration. To obtain a flexible and compatible system, discrete variable and continuous variable QKD protocols are considered to be implemented side by side in the HAPS payload. Depending on the system parameters, it can be beneficial to use the one or the other kind of protocol. Thus, a direct comparison of both in one and the same system is of scientific interest. Each of the protocols has particular requirements on coupling efficiency and implementation. Link budget calculations are performed to analyze possible distances, key rates and data transmission rates for the different schemes. In case of the QKD system, the mean coupling efficiency is of main interest, i.e. signal fluctuations arising from atmospheric turbulence must be taken into account in the security proof, but the buffered key generation relaxes real-time requirements. This is different to classical communications, where the corresponding fading loss must be assessed. A system architecture is presented that comprises the optical aircraft terminal, the optical ground terminal and the most important subsystems that enable implementation of the considered QKD protocols. The aircraft terminal is interfaced with the dedicated quantum transmitter module (Alice) and the ground station with the dedicated quantum receiver module (Bob). The optical interfaces are SMF couplings which put high requirements on the receiving optics, in particular the need for wave-front correction with adaptive optics. The findings of the system study are reviewed and necessary next steps pointed out.

Proceedings Article | 25 September 2017 Open Access

Sota optical downlinks to DLR’s optical ground stations

Christian Fuchs, Dimitar Kolev, Florian Moll, Amita Shrestha, Martin Brechtelsbauer, Fabian Rein, Christopher Schmidt, Maki Akioka, Yasushi Munemasa, Hideki Takenaka, Morio Toyoshima

Proceedings Volume 10562, 1056247 (2017) https://doi.org/10.1117/12.2296107

KEYWORDS: Space telescopes, Telescopes, Satellites, Cameras, Astronomical imaging, Optical tracking, Sensors, Optical communications, Satellite communications, Transponders

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Proceedings Article | 25 September 2017 Open Access

system aspects of optical LEO-to-ground links

D. Giggenbach, A. Shrestha, C. Fuchs, C. Schmidt, F. Moll

Proceedings Volume 10562, 105625N (2017) https://doi.org/10.1117/12.2296054

KEYWORDS: Receivers, Satellites, Signal attenuation, Atmospheric optics, Modulation, Scintillation, Astronomical imaging, Data communications, Sensors, Free space optics

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Proceedings Article | 25 September 2017 Open Access

Inter-island demonstration of optical communication links in robotic operations

Christopher Schmidt, Christian Fuchs, Julio Ramirez, Jorge Pacheco, Martin Brechtelsbauer, Amita Shrestha, Armin Wedler, Philipp Kremer, Vardan Semerjyan, Eric Wille

Proceedings Volume 10562, 105625O (2017) https://doi.org/10.1117/12.2296110

KEYWORDS: Optical communications, Robotics, Control systems, Telecommunications, Space telescopes, Telescopes, Data communications, Astronomical imaging, Video, Lanthanum

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Proceedings Article | 24 February 2017 Presentation + Paper

DLR's free space experimental laser terminal for optical aircraft downlinks

Christian Fuchs, Christopher Schmidt, Benjamin Rödiger, Amita Shrestha, Martin Brechtelsbauer, Julio Ramirez Molina, Jorge Pacheco, Veronika Gstaiger

Proceedings Volume 10096, 1009610 (2017) https://doi.org/10.1117/12.2254791

KEYWORDS: Free space optics, Free space, Laser optics, Laser communications, Telecommunications, Cameras, Forward error correction, Computing systems, Global Positioning System, Telescopes

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Proceedings Article | 21 October 2016 Presentation + Paper

Fading testbed for free-space optical communications

Amita Shrestha, Dirk Giggenbach, Ahmad Mustafa, Jorge Pacheco-Labrador, Julio Ramirez, Fabian Rein

Proceedings Volume 9991, 999105 (2016) https://doi.org/10.1117/12.2239111

KEYWORDS: Free space optics, Free space optical communications, Optical testing, Channel projecting optics, Photodetectors, Calibration, Transmitters, Photovoltaics, Sensors, Signal generators

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Proceedings Article | 29 October 2015 Paper

Ground stations for aeronautical and space laser communications at German Aerospace Center

Florian Moll, Amita Shrestha, Christian Fuchs

Proceedings Volume 9647, 96470I (2015) https://doi.org/10.1117/12.2194093

KEYWORDS: Telescopes, Cameras, Space telescopes, Optical tracking, Acquisition tracking and pointing, Computing systems, Satellites, Telecommunications, Receivers, Mirrors

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Proceedings Article | 17 October 2014 Paper

Demonstration of high-rate laser communications from fast airborne platform: flight campaign and results

Florian Moll, Wolfgang Mitzkus, Joachim Horwath, Amita Shrestha, Martin Brechtelsbauer, Luis Martin, Alberto Lozano, Dionisio Diaz Gonzalez

Proceedings Volume 9248, 92480R (2014) https://doi.org/10.1117/12.2067248

KEYWORDS: Sensors, Laser communications, Free space optics, Fourier transforms, Defense and security, Glasses, Receivers, Dense wavelength division multiplexing, Signal attenuation, Control systems

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Proceedings Article | 24 October 2012 Paper

Transportable optical ground station for high-speed free-space laser communication

Amita Shrestha, Martin Brechtelsbauer

Proceedings Volume 8517, 851706 (2012) https://doi.org/10.1117/12.928966

KEYWORDS: Optical tracking, Global Positioning System, Cameras, Device simulation, Telescopes, Calibration, Control systems, Stars, Computer simulations, Satellites

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Showing 5 of 12 publications

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